Biochemistry. 2019 Jul 9;58(27):2967-2977. doi: 10.1021/acs.biochem.9b00161. Epub 2019 Jun 27.
The RNA-activated protein kinase, PKR, is a key mediator of the innate immunity response to viral infection. Viral double-stranded RNAs induce PKR dimerization and autophosphorylation. The PKR kinase domain forms a back-to-back dimer. However, intermolecular ( trans) autophosphorylation is not feasible in this arrangement. We have obtained PKR kinase structures that resolves this dilemma. The kinase protomers interact via the known back-to-back interface as well as a front-to-front interface that is formed by exchange of activation segments. Mutational analysis of the front-to-front interface support a functional role in PKR activation. Molecular dynamics simulations reveal that the activation segment is highly dynamic in the front-to-front dimer and can adopt conformations conducive to phosphoryl transfer. We propose a mechanism where back-to-back dimerization induces a conformational change that activates PKR to phosphorylate a "substrate" kinase docked in a front-to-front geometry. This mechanism may be relevant to related kinases that phosphorylate the eukaryotic initiation factor eIF2α.
RNA 激活蛋白激酶 PKR 是先天免疫反应病毒感染的关键介质。病毒双链 RNA 诱导 PKR 二聚化和自身磷酸化。PKR 激酶结构域形成背对背二聚体。然而，这种排列方式不允许分子间（trans）自身磷酸化。我们获得了能够解决这一难题的 PKR 激酶结构。激酶原聚体通过已知的背靠背界面以及由激活片段交换形成的前对前界面相互作用。对前对前界面的突变分析支持其在 PKR 激活中的功能作用。分子动力学模拟表明，激活片段在前后二聚体中具有高度动态性，可以采用有利于磷酸转移的构象。我们提出了一种机制，即背靠背二聚化诱导构象变化，从而激活 PKR 磷酸化以“底物”激酶在前后对的几何形状中对接。这种机制可能与磷酸化真核起始因子 eIF2α 的相关激酶有关。
